1. Field of the Invention
The present invention relates to a process for preparing immobilized enzymes or microorganisms. More specifically, the invention is concerned with a process for preparing immobilized enzymes or microorganisms which comprises entrapping enzymes or living microorganisms in a water-insoluble high-molecular weight substance.
2. Description of the Prior Art
Enzymes and microorganisms have recently been extensively used in such fields as the foodstuff industry and the pharmaceutical industry, and have, therefore, acquired renewed importance and interest. According to the conventional prior art processes, the enzymes are dissolved in water and the microorganisms are suspended in water in order to carry out the reaction. Using these methods, however, it is difficult to recover them from the reaction mixture after completion of the reaction. Therefore, the enzymes or microorganisms once used have to be discarded. Because of this, batchwise reaction steps have customarily been employed for reactions using enzymes or microorganisms. Such batchwise reactions render the efficiency of utilizing enzymes or microorganisms very low. Recently, therefore, extensive studies have been made on immobilized enzymes or immobilized microorganisms which can be repeatedly or continuously used for the reaction by rendering enzymes water-insoluble while maintaining their activity or by molding microorganisms into an easy-to-recover size while also retaining their viability.
So far, various reports have appeared on processes for preparing immobilized enzymes or immobilized microorganisms. These processes are roughly divided into (a) an immobilizing process which comprises carrying enzymes or microorganisms on organic or inorganic water-insoluble substances by such means as covalent bonding, ionic bonding, or adsorption; (b) an immobilizing process which comprises covalently-bonding enzymes or microorganisms to one another with bifunctional reagents or the like; and (c) an immobilizing process which comprises entrapping enzymes or microorganisms in water-insoluble high-molecular weight substances hereinafter to be referred to as "entrapping process". Known examples of the entrapping process include a process which comprises dissolving a water-soluble monomer (such as acrylamide, vinylpyrrolidone, hydroxethyl acrylate, or an acrylic acid salt), a water-soluble high-molecular weight substances (such as polyvinyl alcohol or polyacrylamide), or a water-soluble crosslinking agent (such as N, N'-methylenebis((acrylamide))) in water together with enzymes or microorganisms, and then causing the polymerization by the use of polymerization catalysts such as potassium persulfate or by use of radiation such as gamma rays. This process simultaneously imparts a crosslinked structure thereby including the enzymes or microorganisms in the resulting water-insoluble high-molecular weight gel. Another entrapping process is one which comprises dispersing an aqueous solution containing enzymes or microorganisms as fine droplets in an organic solvent having a water-insoluble monomer dissolved therein, and then initiating the polymerization. This encloses the fine water droplets in the resulting water-insoluble polymer. Still a third prior art process comprises dispersing an enzyme--or microorganism--containing aqueous solution as fine water droplets in an organic solvent having a water-insoluble high-molecular weight substance dissolved therein, and then removing the organic solvent to enclose the fine water droplets in the water-insoluble high-molecular weight substance.
Generally, enzymes or microorganisms are relatively stable in water but are unstable in organic solvents, and therefore, the materials frequently used in the conventional entrapping process are soluble in water. The use of water-soluble materials requires a procedure for making them water-insoluble by such means as polymerization or cross-linking, but this procedure inevitably entails the deterioration of the enzymes or microorganisms. The use of water-insoluble high-molecular weight substances as the entrapping materials, on the other hand, requires the use of organic solvents to dissolve them, with the result that the enzymes or microorganisms are deteriorated by the organic solvents.